Electrooptical liquid crystal system

ABSTRACT

To improve switching times, especially at low temperatures, one or more reactive liquid crystalline compounds is added to a liquid crystal mixture used in an electrooptical system. The electrooptical system comprises 
     a PDLC film comprising a liquid crystal mixture forming micro- droplets in an optically isotropic, transparent polymer matrix between 2 electrode layers, 
     one of the refractive indices of the liquid crystal mixture is matched to the refractive index of the polymer matrix, 
     the PDLC film exhibits an electrically switching transparency essentially independent of the polarization of the incident light, 
     the precursor of the PDLC film comprises one or more monomers, oligomers and/or prepolymers and a photoinitiator, and is cured photoradically, 
     the liquid crystal mixture comprises one or more compounds of the formula I                    
      wherein R, A 1 , A 2 , Z 1 , Z 2 , X 1 , X 2 , Q, Y and n are as defined herein.

This is a division, of the application Ser. No. 09/506,815 filed Feb.18. 2000. which is a divisional of Ser No. 09/008,587 filed Jan. 16,1998, which is a divisional of Ser. No. 08/081,820: filed Jun. 25, 1993U.S. Pat. No. 5,871,665, which has U.S. Pat. No. 6,042,745 /EP93/00989filed Apr. 23, 1993.

SUMMARY OF THE INVENTION

The invention relates to an electrooptical liquid crystal system

which between 2 electrode layers contains a PDLC film comprising aliquid crystal mixture forming microdroplets in an optically isotropic,transparent polymer matrix,

in which one of the refractive indices of the liquid crystal mixture ismatched to the refractive index of the polymer matrix,

which exhibits an electrically switchable transparency which isessentially independent of the polarization of the incident light,

the precursor of the PDLC film of which comprises one or more monomers,oligomers and/or prepolymers and a photo-initiator, and is curedphotoradically, and

the liquid crystal mixture of which comprises one or more compounds ofthe formula I

 in which

Z¹ and Z² independently of one another, are a single bond, —CH₂CH₂—,—COO—, —OCO— or —C═C—,

 independently of one another, are trans-1,4-cyclohexylene,1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene,2,3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene and one of

 may also be pyrimidine-2,5-diyl, pyridine-2,5-diyl ortrans-1,3-dioxane-2,5-diyl,

X¹ and X² independently from one another, are H or F,

Q is CF₂, OCF₂, C₂F, OC₂F₄ or a single bond,

Y is H, F, Cl or CN,

n is 0, 1 or 2, and

R is alkyl having up to 13 C atoms, in which one or two non-adjacent CH₂groups can also be replaced by —O— and/or —CH═CH—.

The preparation of PDLC (=polymer dispersed liquid crystal) films isdescribed, for example, in U.S. Pat. No. 4,688,900, Mol. Cryst. Liq.Cryst. Nonlin. Optic, 157, 1988, 427-441, WO 89/06264 and EP 0,272,585.In the so-called PIPS technology (=polymerization-induced phaseseparation) the liquid crystal mixture is first homogenously mixed withmonomers and/or oligomers of the mattix-forming material;phase-separation is then induced by polymerization. Differentiation mustfurther be made between TIPS (temperature-induced phase separation) andSIPS (solvent-induced phase separation) (Mol. Cryst. Liq. Cryst. Inc.Nonlin. Opt. 157 (1988) 427) both being also methods to produce PDLCfilms.

The process of preparation must be controlled very carefully in order toobtain systems with good electrooptical properties. F. G. Yamagishi etal., SPIE Vol. 1080, Liquid Crystal Chemistry, Physics and Applications,1989, p.24 differentiate between a “Swiss cheese” and a “polymer ball”morphology. In the latter one, the polymer matrix consists of smallpolymer particles or “balls” being connected or merging into each otherwhile in the Swiss cheese system, the polymer matrix is continuous andexhibits well defined, more or less spherical voids containing theliquid crystal. The Swiss cheese morphology is preferred because itexhibits a reversible electrooptical characteristic line while thepolymer ball system shows a distinct hysteresis generally leading to adrastic deterioration of the electrooptical characteristic line whencomparing the virgin and the second run.

According to Yamagishi et al., loc. cit., the Swiss cheese morphology ispromoted in case the polymerization reaction runs via a step mechanism,and in WO 89/06264 it is pointed out that the step mechanism is favoredin case the precursor of the polymer matrix consists of multifunctionalacrylates and multifunctional mercaptanes.

In PDLC films, one of the refractive indices of the liquid crystalmixture, customarily the ordinary refractive index no, is selected insuch a way that it more or less coincides with the refractive indexn_(p) of the polymeric matrix. If no voltage is applied to theelectrodes, the liquid crystal molecules in the droplets exhibit adistorted alignment, and incident light is scattered at the phaseboundary between the polymeric and liquid crystal phases.

On applying a voltage, the liquid crystal molecules are aligned parallelto the field and perpendicular to the E vector of the transmitted light.Normally incident light (viewing angle θ=0°) now sees an opticallyisotropic medium and appears transparent.

No polarizers are required for operating PDLC systems, as a result ofwhich these systems have high transmission. PDLC systems provided withactive matrix addressing have been proposed on the basis of thesefavorable transmission properties in particular for projectionapplications, but in addition also for displays having high informationcontent an for further applications.

The liquid crystal mixtures used for producing PDLC systems have to meeta wide range of demands. One of the refractive indices of the liquidcrystal mixture is selected such that it matches with the refractiveindex of the polymer matrix. The term matching of refractive indicesused here covers not only the case n_(o) (resp. another refractive indexof the liquid crystal mixture)˜n_(p), but also the condition n_(o)(resp. another refractive index of the liquid crystal mixture)<n_(p)which is sometimes chosen to reduce off-axis haze and enlarge the viewangle as is described, for example, in EP 0,409,442.

The liquid crystal mixture preferably has a positive dielectricalanisotropy but the use of dielectrically negative liquid crystalmixtures (see, for example, WO 91/01511) or two-frequency liquid crystalmixtures (see, for example, N.A. Vaz et al., J. Appl. Phys. 65, 1989,5043) is also discussed.

Furthermore, the liquid crystal mixture should have a high clearingpoint, a broad nematic range, no smectic phases down to low temperaturesand a high stability and should be distinguished by an opticalanisotropy Δn and a flow viscosity η which can be optimized with respectto the particular application, and by a high electrical anisotropy.

A series of matrix materials and polymerization processes have hithertobeen proposed for producing PDLC systems. The PIPS, SIPS and TIPStechnologies are described in some detail in Mol. Cryst. Liq. Cryst.Inc. Nonlin. Optics, 157, 1988, 427. The PDLC systems described in Vol.Cryst. Liq. Cryst.

Inc. Nonlin. Optics, 157, 1988, 427 are based on an epoxy film, while inEP. 0,272,585 acrylate systems are given. The PDLC system of WO 89/06264is based on multifunctional acrylates and multifunctional thioles, andY. Hirai et al., SPIE Vol. 1257, Liquid Crystal Displays andApplications, 1990, p.2 describe PDLC systems the precursor of thepolymer matrix of which being based on monomers and oligomers. Furthersuitable matrix materials are described, for example, in U.S. Pat. No.3,935,337, WO 91/13126 and in further references.

Electrooptical systems containing PDLC films can be addressed passivelyor actively. Active driving schemes employing an active matrix havingnonlinear addressing elements like, for example, TFT transistorsintegrated with the image point, are especially useful for displays withhigh information content.

When the PDLC system is addressed by means of an active matrix, afurther far reaching criterion is added to the requirements listed sofar which must be fulfilled by the cured polymer and the liquid crystalmixture being embedded in microdroplets. This is related to the factthat each image point represents a capacitive load with respect to theparticular active nonlinear element, which is charged at the rhythm ofthe addressing cycle. In this cycle, it is of paramount importance thatthe voltage applied to an addressed image point drops only slightlyuntil the image point is again charged in the next addressing cycle. Aquantitative measure of the drop in voltage applied to an image point isthe so-called holding ratio (HR) which is defined as the ratio of thedrop in voltage across an image point in the nonaddressed state and thevoltage applied; a process for determining the HR is given, for example,in Rieger, B. et al., Conference Proceeding der Freiburger ArbeitstagungFlüssigkristalle (Freiburg Symposium on Liquid Crystals), Freiburg 1989.Electrooptical systems having a low or relatively low HR showinsufficient contrast.

A further serious problem is often that the liquid crystal mixture hasinsufficient miscibility with the monomers, oligomers and/or prepolymersof the polymer used for forming the matrix, which limits in particularthe use of PIPS technology in microdroplet matrix systems.

A further disadvantage is in particular that the liquid crystal mixtureor individual components of the liquid crystal mixture are in many casesdistinguished by an excessively high and/or significantly temperaturedependent solubility in the cured, matrix-forming polymer. If, forexample, the solubility or the temperature-dependence of the solubilityof one or several components differs quite significantly from that ofthe remaining components, it may happen that the physical properties ofthe mixture and in particular also of the refractive indices n_(e) andn_(o) are substantially affected, which disturbs the adjustment of n_(o)or n_(e) or another refractive index of the liquid crystal mixture ton_(m), thus resulting in a deterioration of the optical properties ofthe system.

The “bleeding” described in EP 0,357,234, according to which at leastsome of the liquid crystal droplets have the tendency, when the matrixfilm is subjected to mechanical stress, to dissolve with diffusion ofthe liquid crystal to the film surface or into the matrix, is favorableby a high solubility of the liquid crystal mixture in the cured polymer.

Very important electrooptical parameters of electrooptical systemsmentioned above are the switching voltages and switching times. Thethreshold voltage V_(th) is usually defined as the voltage V_(10,0,20)at which a transmission of 10% is observed at a temperature of 20° C.and under a viewing angle ⊖ of 0° while the saturation voltage is thelowest voltage for which the maximum transmission is observed at 20° C.and a viewing angle of 0°. The switching on time t_(on) is usuallyreported as the time necessary for the transmission to rise from 0% to90% of the maximum transmission when the saturation voltage is appliedwhile t_(off) is the time necessary for the transmission to drop from100% to 10% when the voltage is switched off.

In U.S. Pat. No. 4,673,255 it is shown that a correlation exists betweenthe mean size of the microdroplets on the one hand and the switchingvoltages and switching times of the system on the other hand. Generally,relatively small microdroplets cause relatively high switching voltages,but relatively short switching times and vice versa.

Experimental methods for influencing the average droplet size aredescribed, for example, in U.S. Pat. No. 4,673,255 and in J. L. West,Mol. Cryst. Liq. Cryst. Inc. Nonlin. Opt., 157, 1988, 427. In U.S., Pat.No. 4,673,255, average drop diameters between 0.1 μm and 8 μm are given,while, for example, a matrix which is based on a glass monolith haspores having a diameter between 15 and 2,000 Å. For the mesh width ofthe network of PN systems, a preferred range between 0.5 and 2 μm isgiven in EP 0,313,053.

The switching voltage, however, must not be chosen too high because ofseveral reasons (power consumption, safety of operation, compatibilitywith conventional modules of microeletronic).

On the other hand, high switching times are generally not tolerablewhich is evident in case of display applications, but which is also truefor many other applications. Low switching time are also often requiredat lower temperature because the systems according to the preamble arealso discussed for out-door applications.

It is true that considerable efforts have already been undertakenhitherto in order to optimize PDLC systems with respect to the liquidcrystal mixture used and the polymer system. On the other hand, however,it is still an open problem how to realize PDLC films which arecharacterized both by low switching times especially at low temperaturesand at the same time by advantageous values of the switching voltages.No method is known so far by which switching voltages and switchingtimes can be adjusted with respect to the intended application more orless independently from each other.

Furthermore, only few investigations of PDLC systems having activematrix addressing can be found in the literature, and no concepts haveso far been proposed for providing electrooptical systems having

a high HR and a low temperature dependence of HR

advantageous values of the switching voltages, and

low switching times, especially at low temperatures.

Consequently, there is a high demand for PDLC systems which fulfill to alarge extent the requirements described and which exhibit advantageousvalues of the switching voltages, and, in particular, low switchingtimes especially at low temperatures. Furthermore, there is a highdemand for actively addressed PDLC systems which exhibit a high HR and alow temperature dependence of HR in addition to low switching times.

The object of the invention was to provide PDLC systems of this type andprecursors of these PDLC systems containing monomers, oligomers and/orprepolymers of the polymer used and a liquid crystal mixture. Other aimsof the present invention are immediately evident to the person skilledin the art from the following detailed description.

It has been found that PDLC systems which are characterized by lowswitching times can be obtained if one or more reactive liquidcrystalline compounds are added to its liquid crystal mixture.

The invention thus relates to an electrooptical liquid crystal system

which between 2 electrode layers contains a PDLC film comprising aliquid crystal mixture forming microdroplets in an optically isotropic,transparent polymer matrix,

in which one of the refractive indices of the liquid crystal mixture ismatched to the refractive index of the polymer matrix,

which exhibits an electrically switchable transparency which isessentially independent of the polarization of the incident light,

the precursor of the PDLC film of which comprises one or more monomers,oligomers and/or prepolymers and a photoinitiator, and is curedphotoradically, and

the liquid crystal mixture of which comprises one or more compounds ofthe formula I

 in which

Z¹ and Z² independently of one another, are a single bond, —CH₂CH₂—,—COO—, —OCO—or —C═C—,

 independently of one another, are trans-1,4-cyclohexylene,1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene,2,3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene and one of

 may also be pyrimidine-2,5-diyl, pyridine-2,5-diyl ortrans-1,3-dioxane-2,5-diyl,

X¹ and X² independently from one another, are H or F,

Q is CF₂, OCF₂, C₂F₄ or a single bond,

Y is H, F, Cl or CN,

n is 0, 1 or 2, and

R is alkyl having up to 13 C atoms, in which one or two non-adjacent CH₂groups can also be replaced by —O— and/or —CH═CH—,

characterized in that the liquid crystal mixture additionally contains.one or more reactive liquid crystalline compounds in order to obtainimproved switching times especially at low temperatures. Part of thereactive liquid crystalline compounds which can be used in theelectrooptical systems according to the present invention are new, andsuch new reactive liquid crystalline compounds are also claimed.

Specifically, the present invention also relates to reactive liquidcrystalline compounds of formula III

R¹—P—X—A³—Z—A⁴—R²  III

COO— with W being H, Cl or alkyl with 1-5 C atoms and m being 1-7,

P is alkylene with up to 12 C atoms, it being also possible for one ormore CH₂ groups to be replaced by O,

X is —O—, —S—, —COO—, —OCO— or a single bond,

R² is alkyl radical with up to 15 C atoms which is unsubstituted,mono-or polysubstituted by halogen, it being also possible for one ormore CH₂ groups in these radicals to be replaced, in each caseindependently of one another, by —O—, —S—, —CO—, —OCO—, —CO—O— or—O—CO—O— in such a manner that oxygen atoms are not linked directly toone another, —CN, —F, —Cl, or alternatively R² has one of the meaningsgiven for R¹-P-X,

A³ is a 1,4-phenylene or a napthalene-2,6-diyl radical which isunsubstituted or substituted with 1 to 4 halogen atoms,

A⁴ is

 it being possible for radicals (a) and (b) to be substituted by CN orhalogen and one of the 1,4-phenylene groups in (a) and (b) can also bereplaced by a 1,4-phenylene radical in which one or two CH groups arereplaced by N, and

Z is —CO—O—, —O—CO—, —CH₂CH₂— or a single bond.

The construction of the electrooptical system according to the presentinvention corresponds to the customary mode of construction for systemsof this type. The term customary mode of construction is in this casebroadly interpreted and includes all adaptations and modifications.

Thus, for example, the matrix formed by the transparent medium in whichthe liquid crystal mixture is microdispersed or microencapsulated, isarranged between conducting electrodes like a sandwich.

The electrodes are applied, inter alia, to substrate sheets of, forexample, glass, plastic or the like; if desired, however, the matrix canalso be provided directly with electrodes so that the use of substratescan be avoided. One of the electrodes forms an active matrix while theother one acts as counter electrode.

The precursor of the PDLC film comprising the precursor of the matrix,the liquid crystal mixture and one or more reactive liquid crystallinecompounds can be capillary filled between two substrates which areprovided with electrode layers, and the precursor of the PDLC film issubsequently cured, for example, by irradiation with UV light. Anothertechnique comprises coating of the precursor of the PDLC film on asubstrate with subsequent curing. The film may be peeled off andarranged between 2 substrates provided with electrode layers. It is alsopossible that the substrate onto which the precursor of the PDLC film isapplied exhibits an electrode layer so that the electrooptical systemcan be obtained by applying a second electrode layer and, optionally, asecond substrate onto the coated and cured film.

The electrooptical system according to the invention can be operatedreflectively or tramsmissively so that at least one electrode and, ifpresent, the associated subs-rate are transparent. Both systemscustomarily contain no polarizers, as a result of which a distinctlyhigher light transmission results. Furthermore, no orientation layersare necessary, which is a considerable technological simplification inthe production of these systems compared with conventional liquidcrystal systems such as, for example, TN or STN cells.

Processes for the production of PDLC films are described, for example,in U.S. Pat. No. 4,688,900, U.S. Pat. No. 4,673,255, U.S. Pat. No.4,671,618, WO 85/0426, U.S. Pat. No. 4,435,047, EP 0,272,595, Mol.Cryst. Liq. Cryst, Inc. Nonlin. Opt. 157 (1988) 127, Liquid Crystals, 3(1988) 1543, EP 0,165,063, EP 0,345,029, EP 0,357,234 and EP 0,205,261.The formation of the PDLC film is generally achieved by 3 basic methods:in the PIPS technique (=PIPS, polymerization induced phase separation)the liquid crystal mixture, and optionally further additives, aredissolved in the precursor of the matrix material, and subsequentlypolymerization is started. TIPS (=thermally induced phase separation)means that the liquid crystal mixture is dissolved in the melt of thepolymer followed by cooling while SIPS (=solvent induced phaseseparation) starts with dissolving the polymer and the liquid crystalmixture in a solvent with subsequent evaporation of the solvent. Theinvention is, however, not restricted to these specific techniques butcovers also electrooptical systems obtained by modified methods or othermethods. The use of the PIPS technology is usually preferred.

The thickness d of the electrooptical system is customarily chosen to besmall in order to achieve a threshold voltage V^(th) which is as low aspossible. Thus, for example, layer thicknesses of 0.8 and 1.6 mm arereported in U.S. Pat. No. 4,435,047, while values for the layerthickness between 10 and 300 μm are given in U.S. Pat. No. 4,688,900 andbetween 5 and 30 μm in EP 0,313,053. The electrooptical systemsaccording to the invention only have layer thicknesses d greater than afew mm in exceptional cases; layer thicknesses below 200 μm andespecially below 100 μm are preferred. In particular, the layerthickness is between 2 and 190 μn, especially between 3 and 50 μn andvery particularly between 3 and 25 μm.

An essential difference between the electrooptical liquid crystal systemaccording to the present invention and those customary hitherto,however, consists in that the liquid crystal mixture contains one ormore reactive liquid crystalline compounds.

The term reactive liquid crystalline compounds denotes rod-likecompounds of formula II

R′—G′—R″  II

wherein at least one of the terminal groups R′ and R″ is a reactivegroup exhibiting one reaction site such as a hydroxyl group HOW′₂C—, athiol group HSW′₂C—, an amino group HW′N—, a carboxyl group, an epoxidegroup

or an isocyanate group O═C—N—, or a polymerizable reactive groupexhibiting two or more reactive sites such a; vinyl type groupW′₂C═CW′—, a (meth)acrylate type group

a styrene type group

with W′ being independently from each other H or an alkyl group with 1-5C atoms,

the other terminal group is also, independently from the first terminalgroup, a reactive group with one or more reactive sites or an alkylradical with up to 15 C atoms which is unsubstituted or mono- orpolysubstituted by halogen, it being also possible for one or more CH₂groups in these radicals to be replaced, in each case independently ofone another, by —O—, —S—, —CO—, —OCO—, —CO— O— or —O—CO—O— in such amanner that O atoms are not linked directly to one another,

G′ is a rod-like diyl group of the formula

—S₁—(A⁵—Z³)_(m)—A⁶—S²—

with S₁ and S² being independently from each other alkylene groups with0-20 C atoms which can be linear or branched, it also being possible forone or more CH₂ groups to be replaced, in each case independently fromeach other, by —O—, —CO—, —S— or —NW′— with the proviso that O atoms arenot linked directly to one another,

A⁵ and A⁶ denote, independently from each other,

a) a cyclohexylene group, wherein one or two non-adjacent CH₂ groups maybe replaced by O or S atoms,

b) an unsubstituted 1,4-phenylene group wherein one to three CH groupsmay be replaced by —N— or a 1,4-phenylene group which is mono- orpolysubstituted by F, Cl and/or CH₃,

c) a bicyclo(2,2,2)octylene group, a naphthaline-2,6-diyl group, adecahydronaphthaline-2,6-diyl group or 1,2,3,4-tetrahydronaphthalinegroup,

Z³ is independently from each other —CO—O—, —O—CO—, —CH₂CH₂—, —CH₂O—,—OCH₂—, —C≡C— or a single bond, ant

m denotes 1,2,3, or 4.

Above and below, the term reactive liquid crystalline compounds refersto reactive rod-like molecules like, for example, those of formula IIIor other rod-like reactive compounds which may be enantiotropic,monotropic or isotropic, preferably, however, enantiotropic ormonotropic.

In a preferred embodiment of the eletrooptical systems according to thepresent invention, at least one of R′ and R″ preferably is or containsan ene-group

When polymerizing the precursor of the PDLC film by impact of thermalenergy or irradiation, usually in presence of an ionic or radicalpolymerization initiator, the reactive liquid crystalline compoundsbeing contained in the liquid crystalline phase when phase separationstarts, are reacted with each other thus obviously forming some internalstructure in the liquid crystalline microdroplets. This structure may beconsidered as some kind of network which divides the liquid crystallinemicrodroplet in some smaller sub-compartments which may be in contactwith each or be separated from each other. The term “some kind ofnetwork” is to be understood in a wide sense and comprises a wide rangeof geometries of the internal structure. The surrounding polymer matrixand the internal structure may be connected or not.

In another embodiment of the electrooptical systems according to thepresent invention, at least one of R′ and R″ is a reactive groupexhibiting one reactive site, and in particular a hydroxyl group, athiol group, a carboxyl group, an amino group or an isocyanato group.Reactive liquid crystalline compounds of this type can be attached tothe surrounding polymeric matrix in a coupling reaction or they can alsoreact with each other, especially in case of suitably chosen co-reactivecompounds of formula II. The coupling reaction may occur during thepolymerization of the surrounding matrix or afterwards as apolymer-analogous reaction. In case of reactive liquid crystallinecompounds of formula II exhibiting only one reactive group of the onereaction site type, it is assumed that the reactive group is coupled tothe inner surface of the polymeric matrix with the rest of the moleculebeing arranged in the liquid crystalline microdroplet, inducing theresame kind of internal structure.

The addition of one or more reactive liquid crystalline compounds offormula II exhibiting two reactive groups R′ and R″ to the liquidcrystalline mixture is generally preferred. Also preferred is theaddition of a reactive liquid crystalline component, containing at leasttwo different reactive liquid crystalline compounds according to formulaII at least one of which contains 2 reactive groups R′ and R″ . Reactiveliquid crystalline components containing at least one reactive liquidcrystalline compound with one reactive group R′ (monofunctional reactiveliquid crystalline compound) and at least one reactive liquidcrystalline co-pound with two reactive compounds (difunctional reactiveliquid crystalline compound) often are especially preferred whilereactive liquid crystalline components consisting of one or moremonofunctional reactive liquid crystalline compounds usually are lessadvantageous.

Especially preferred difunctional reactive liquid crystalline compoundsare di-ene type compounds such as divinyls, diacrylates ordimethacrylates, furthermore diols, dithiols and diisocyanates, but alsocompounds with different reactive groups such as ene-ols, ene-thiols,vinylacrylates etc.

The groups S¹ and S² acting as spacer groups between the reactive groupsR′ and R″ and the mesogenic core (A⁵—Z³)_(m)—A⁶—are independently fromeach other an alkylene group with 0-20 C atoms which can be linear orbranched, it also being possible for one or more CH₂ groups to bereplaced, in each case independently from each other by —O—, —CO—, —S—or —NW′— with the proviso that oxygen atoms are not linked directly toone another.

The length and the structure of the groups S¹ and S² determine whetherthe mesogenic group exhibits a more or less pronounced degree offlexibility. The following list of suitable groups S¹ and S² is intendedto be illustrative and not limiting:

ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene,decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene,methyleneoxybutylene, ethylenethioethylene,ethylene-N-methyliminoethylene, (1-oxy)methyleneoyloxy,(2-oxy)ethyleneoyloxy, (3-oxy)propyleneoyloxy, (4-oxy)butyleneoyloxy,(5-oxy)pentyleneoyloxy, (6-oxy)hexyl-eneoyloxy, (7-oxy)heptyleneoyloxy,(8-oxy)octyleneoyloxy, (1-oxy)methyleneoxycarbonyl(2-oxy)ethyleneoxycarbonyl, (3-oxy)propyleneoxycarbonyl,(4-oxy)butyleneoxycarbonyl, (5-oxy)pentyleneoxycarbonyl,(6-oxy)hexyleneoxycarbonyl, (7-oxy)heptyleneoxycarbonyl and(8-oxy)octyleneoxycarbonyl.

The mesogenic core, —(A⁵—Z³)_(m)—A⁶— of the reactive liquid crystallinecompounds can exhibit 2, 3, 4 or 5 rings:

—A⁵—Z³—A⁶—  (1)

—A⁵—Z³—A⁵—Z³—A⁶—  (2)

—A⁵—Z³—A⁵—Z³—A⁵—Z³—A⁶—  (3)

—A⁵—Z³—A⁵—Z³—A⁵—Z³—A⁵—Z³—A⁶—  (4)

Especially preferred for use in the electrooptical systems according tothe present invention are reactive liquid crystalline compoundsexhibiting 2-, 3- or 4-ring mesogenic groups according to formula(1)-(3) and in particular 2- or 3-ring mesogenic groups according toformula (1) or (2).

In the following, for sake of simplicity, Cyc is a 1,4-cyclohexylenegroup, Phe is a 1,4-phenylene group which can be unsubstituted or mono-,di- or trifluorinated, Dio is a 1,3-dioxane-2,5-diyl group, Pyd is apyridine-2,5-diyl group, Pyr is a pyrimidine-2,5-diyl group, Pip is apiper dine-1,4-diyl group, Bio is a 1,4-bicyclo(2,2,2)octylene group,Nap is

a naphthalene-3,6-diyl group and Thn is a1,2,3,4-tetrahydronaphthalene-2,6-diyl group; the abbreviations Dio,Pyd, Pyr and Pip comprise all possible positional isomers.

Especially preferred is the following smaller group of mesogenic coresaccording to formula (2):

-Phe-Z³-Phe-  (2)a

-Cyc-Z³-Cyc-  (2)b

-Phe-Z³-Cyc-  (2)c

-Pyr-Z³-Phe-  (2)d

-Pyd-Z³-Phe-  (2)e

-Dio-Z³-Cyc-  (2)f

In the structures according to formulae (2)a-(2)f Z³ preferably is—COO—, —OCO—, —CH₂CH₂— or a single bond. Electrooptical systemsaccording to the present invention containing one or more reactiveliquid crystalline compounds containing a two-ring mesogenic structureaccording to formulae (2)a-(2)c generally exhibit especiallyadvantageous properties.

Especially preferred is also the use of reactive liquid crystallinecompounds according to formula II which contain a mesogenic group with 3rings according to formulae (3)a-(3)f:

-Phe-Z³-Phe-Z³-Phe-  (3)a

-Cyc-Z³-Phe-Z³-Phe-  (3)b

-Cyc-Z³-Cyc-Z³-Phe-  (3)c

 -Cyc-Z³-Cyc-Z³-Cyc-  (3)d

-Pyr-Z³-Phe-Z³-Phe-  (3)e

-Pyd-Z³-Phe-Z³-Phe-  (3)f

Electrooptical systems containing both at least one 2-ring reactiveliquid crystalline compound with a mesogenic group according to formula2(a)-2(f) and at least one 3-ring reactive liquid crystalline compoundwith a mesogenic group according to formulae 3(a)-3(f) are preferred.

In the mesogenic structures of formulae (3)a-(3)f Z³ preferably isindependently from each other a single bond, —COO—, —OCO— or —CH₂CH₂—.Especially preferred are the following combinations with—representing asingle bond:

first linking group second linking group — — — CH₂CH₂ CH₂CH₂ CH₂CH₂ OCOCOO

Electrooptical systems containing one or Lore reactive liquidcrystalline compounds according to formula II which contain a mesogenicgroup with 4 rings according to formulae (4)a-(4)f exhibit advantageousproperties:

 -Cyc-Z³-Phe-Z³-Phe-Z³-Phe-  (4) a

-Cyc-Z³-Cyc-Z³-Phe-Z³-Phe-  (4)b

-Cyc-Z³-Cyc-Z³-Cyc-Z³-Phe-  (4)c

-Cyc-Z³-Phe-Z³-Phe-Z³-Cyc-  (4)d

-Phe-Z³-Phe-Z³-Phe-Z³-Phe-  (4)e

-Cyc-Z³-Cyc-Z³-Cyc-Z³-Cyc-  (4)f

In the structures according to formula (4)a-(4)f at least one of Z³preferably is a single bond. The other two linking groups preferablydenote independently from each other a single bond, —COO—, —OCO— OR—CH₂CH₂—.

Reactive liquid crystalline compounds have hitherto been known. EP0,261,712, for example, describes liquid crystalline diacrylates of theformula

wherein R is a hydrogen atom or a methyl group, Z′ is independently fromeach other —COO— or —OCO— (≡—OOC), and B is a flexible spacer, chosenfrom the group consisting of —(CH₂)_(x)—, —(CH₂))_(x)—O—,—(Si(CH₃)₂—O)_(x)— wherein x=1-5 or —(CH₂—CH₂—O)_(y)—O— wherein y=1-8,for use in orientation layers of LCDs.

Hikmet describes in Mol. Cryst. Liq. Cryst., 198, 357-70 anisotropicgels which were obtained by curing a mixture of a low-molecular weightliquid crystal and liquid crystalline diacrylates.

The use of reactive liquid crystalline compounds in PDLC systems,however, is not reported in literature and it was completely surprisingthat PDLC systems the liquid crystalline mixture of which additionallycontains one or more reactive liquid crystalline compounds, exhibitsshort switching times even at low temperature and simultaneouslyadvantageous values of the switching voltages.

In the following table 1, the electrooptical properties of systemsaccording to the invention are compared with the properties of aconventional PDLC system (comparative example 1) resp. with theproperties of PDLC systems containing non liquid-crystalline reactivemonomers. NOA 65 (prepared by Norland Products) is used as the precursorof the matrix, and E7 from Merck Ltd., GB, which consists of

51.0% of 4-pentyl-4′-cyanobiphenyl

25.0% of 4-heptyl-4′-cyanobiphenyl

16.0% of 4-octoxy-4′-cyanobiphenyl

8.0% of 4-pentyl-4″-cyanoterphenyl

is used as liquid crystalline mixture. The additives used in therespective experiments, and their amount with respect to the mass of theprecursor of the PDLC film are given in table 1. The systems in eachcase are prepared by mixing and optionally heating the constituents ofthe precursor of the PDLC film to form a clear solution whichsubsequently is capillary filled together with spacers be:ween 2 glasssubstrates which are provided with electrode layers. The system is thenirradiated with light of suitable wavelength in order to cure theprecursor; NOA 65 the composition of which is given in MolecularCrystals Liquid Crystals, 196 (1991), 89-102, contains benzophenone as aphotoinitiator. The response time τ given in table 1 which is the sum ofswitching on and switching off times, is measured at a drive voltage of1.5×V_(sat) with V_(sat) being the lowest voltage for which maximumtransmission is observed.

It is evident from table 1 that the addition of non-liquid crystallinereactive compounds to the precursor of the PDLC film does not affect theelectrooptical properties of the cured PDLC film very much (comparativeexperiments no. 2 and no. 3). Both the saturation voltage and theswitching times are comparable to the values obtained for a conventionalsystem without any reactive additives (comparative experiment no. 1).The reason most presumably is that the non-liquid crystalline reactiveadditives are incorporated into the polymer matrix and do not give riseto an internal structure of the liquid crystalline microdroplets.

Contrary to this, experiments no. 1-4 show that a drastical reduction ofswitching times is obtained in case a reactive liquid crystallinecompound is added to the precursor of the PDLC film. Especiallypronounced is the reduction of switching time at the lower temperatureof 0° C. While the conventional PDLC system of comparative experimentno. 1 exhibits a switching time τ (0° C.)=283 ms, the switching times ofthe systems according to the invention as prepared in experiments no.2-4 exhibit switching times at 0° C. between 10 and 47 ms.

TABLE 1 Composition of the precursor of the PDLC film Electroopticalproperties Percentage Percentage Percentage Experiments of NOA 65 of E 7Reactive additive reactive τ (20° C.)/ms τ (0° C.)/ms V_(sat)/VComparative 40% 60%   — — 33 283 19 experiment No. 1 Comparative 40% 58%bisphenol A diacrylate 2% 48 191 24 experiment No. 2 Comparativeexperiment No. 3 40% 58%

2% 41 326 17 Experiment No. 1 40% 58%

2% 10 30 70 Experiment No. 2 40% 58%

2%  3 10 80 Experiment No. 3 40% 59.5%

0.5% 16 28 43 Experiment No. 4 40% 59.9%

0.1% 31 47 28

When comparing experiments no. 2-4 it can be concluded that the additionof a diacrylate component has contrary effects with respect to switchingtimes and switching voltages. If the concentration of the diacrylatecompound

is chosen to be 2% with respect to the mass of the precursor of th PDLCfilm, the switching times both at 20° C. and 0° C. are very low whilethe saturation voltage is relatively high and distinctly higher than thesaturation voltage of the conventional system according to comparativeexperiment no. 1.

Reducing the concentration of the diacrylate compound as low as 0.1%gives a saturation voltage of28 V which is comparable to the saturationvoltage of the conventional system according to comparative experimentno. 1, but a distinctly lower switching time especially at 0° C. Theconditions of preparation are the same in all experiments listed intable 1 (mixing temperature of the precursor of the PDLC matrix, coolingrate, etc.) so that the distribution of microdroplet diameters can beassumed to be more or less the same.

Table 2 summarizes the electrooptical properties of systems each of themcontaining only one monofunctional reactive liquid crystalline compound.It can be taken from table 2 that the addition of monofunctionalreactive liquid crystalline compounds alone is often less advantageous.Both in experiment no. 5 and no. 6 the switching Mimes at least of 0° C.are inferior to the switching times of the conventional PDLC systemaccording to comparative experiment No. 1. Especially disadvantageous isoften the addition of monofunctional reactive liquid crystallinecompounds wherein the non-reactive terminal group is a nitrile group.The use of monofunctional reactive liquid crystalline compounds with aless polar or unpolar non-reactive terminal group such as F. Cl, CF₃,OCF₃, OCHF₂, alkyl or alkoxy, however, and/or the use of reactive liquidcrystalline components containing at least one difunctional and at leastone monofunctional liquid crystalline compound, is often preferred.

TABLE 2 Composition of the precursor of the PDLC film PercentagePercentage Experiments of NOA 65 of E 7 Reactive additive Experiment No.5 40% 58%

Experiment No. 6 40% 58%

Electrooptical properties Percentage Experiments reactive τ (20° C.)/msτ (0° C.)/ms V_(sat)/V Experiment No. 5 2%  31 >500 50 Experiment No. 62% 500 — 13

Based on the experiments summarized in table 1 and 2 as well as onfurther extensive experimental studies, the present inventors havedeveloped the following ideas in order to explain the effects observedwhen adding reactive liquid crystalline compounds to the precursor ofthe PDLC film:

The reactive liquid crystalline compounds which are completely soluble(i.e., soluble at any concentration ratio of liquid crystal mixture andreactive additive) or at least highly soluble in the liquid crystalmixture, are polymerized and form a network or some other kind ofstructure within the droplets. The switching times are the lower themore close-meshed the substructure is. The reactive liquid crystallinecompound binds into the interface of polymeric matrix and liquid crystalmicro-droplet which results in increased anchoring and hence restoringforces on the components of the liquid crystal mixture. This leads to anincrease of the switching voltages which is the more pronounced thehigher the concentration of the reactive liquid crystalline compoundsis. The concentration of the reactive liquid crystalline component hastherefore to be adjusted properly in order to realize a drasticalreduction of switching times in connection with no or only a tolerableincrease in switching voltages.

The explanation outlined is to be understood as hypothesis which doesnot restrict the present invention.

In extensive experiments it was found out that the concentration of thereactive liquid crystalline component which consists of one or morereactive liquid crystalline compounds, must not be chosen too high andpreferably is not more than 5% and especially less than 2.5% withrespect to the mass of the precursor of the PDLC film. Particularlypreferred are electrooptical systems according to the present inventionthe reactive liquid crystalline component of which amounts to not morethan 1%.

The reactive liquid crystalline compounds can be chosen from the greatpool of known and new reactive liquid crystalline compounds embraced byformula II. The reactive liquid crystalline compounds preferably exhibita high or very high solubility in the liquid crystal mixture.

The reactive liquid crystalline component preferably contains not morethan 10 and in particular not more than 5 reactive crystallinecompounds. Difunctional reactive liquid crystalline compounds aregenerally preferred and in case of these compounds, the reactive liquidcrystalline component preferably contains 1-6, especially 1-3 and inparticular not more than 2 reactive liquid crystalline compounds.Further preferred are reactive liquid crystalline components comprisingat least one difunctional and one monofunctional reactive liquidcrystalline compound. Further preferred are reactive liquid crystallinecomponents comprising at least one monofunctional reactive liquidcrystalline compound with the second terminal group being F, Cl, CF₃,OCF₃, OCHF₂ or non-polar group such as alkyl or alkoxy.

The present inventors further observed that electrooptical systemsaccording to the present invention are characterized by advantageouselectrooptical properties and that they exhibits, in particular, no oronly very little memory effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 each illustrate electrooptical characteristic lines ofconventional electrooptical systems; and

FIGS. 4-6 illustrate electrooptical characteristic lines ofelectrooptical systems according to the invention.

DETAILED DESCRIPTION

This memory effect which is often observed with conventionalelectrooptical systems the liquid crystal mixture of which contains noreactive liquid crystalline compounds, can be seen in FIGS. 1-3 givingelectrooptical characteristical lines for a conventional system theprecursor of which has the following composition:

Liquid crystal mixture 60% of BL036 Precursor of the matrix 3.96% ofTMPTMP 18.0% of EHA 4.8% of HDDA 12.24% of E 270 1.0% of D 1173(photo-initiator)

BL036 is a liquid crystal mixture available through ML, Poole, GB;TMPTMP is trimethylolpropanetri(3-mercaptopropionate); EHA is2-ethyl-hexanolacrylate; HDDA is hexanedioldiacrylate, E 270 is acommercially available oligomer (Ebecryl 270, aliphatic urethanediacrylate, molecular weight ≈1,200) and D 1173 is Darocur 1173available through E. Merck, Darmstadt.

FIG. 1 shows the electrooptical characteristic line for this system at20° C. (=20 μm); it exhibits an excellent electrooptical behavior and nomemory effect: when switched on and off, the system has the sameoff-state transmission (or better opacity) as in the initial unswitchedstate.

The situation changes for higher temperatures. This can be seen fromFIG. 2 which shows an electrooptical curve and the off-statetransmission for the same system at 70° C. When switched off, thetransmission is not as low as in the initial, unswitched state. Thiseffect which is observed for most conventional systems especially athigher temperature is termed as memory effect.

FIG. 3 shows electrooptical curves for this system at 70° C. which wererecorded after the off-switching in FIG. 2. When re-switched, thetransmission starts at the high level of FIG. 2 and stops at this levelduring subsequent operations.

The system can be fully recovered only when it is being cooled to lowertemperatures of, for example, 20° C. but the effect appears again whenreturning to higher temperatures of operation.

This effect is especially disadvantageous if the electrooptical systemis to be operated over a wide range of temperatures, like, for example,in the case of out-door displays, transportable computers etc.

The present inventors now found that the electrooptical systemsaccording to the present invention are characterized by a drasticallyreduced memory effect as can be seen from FIG. 4 showing anelectrooptical characteristic line for a system according to the presentinvention the precursor of which contains 59.8% of BL036, 0.2% of

and the same precursor of the matrix used for the conventional systemsof FIGS. 1-3; d 20 μm. FIG. 5 shows the electroptical characteristicline for this system according to the present invention at 20° C., whichis excellent and only shows a slight increase with respect to V_(sat)when compared to the system of FIG. 1. The properties of the systems ofFIG. 1 and FIG. 5 are compared in the following table with T_(on) resp.T_(off) being on-state resp. off-state transmission.

V_(sat) T_(on) T_(off) System of FIG. 1 23.6 0.185 0.004 System of FIG.5 30.1 0.874 0.005

The memory effect can be completely suppressed if the concentration ofthe reactive liquid crystalline component is chosen to be higher, as canbe seen from FIG. 6. This Fig. shows an electrooptical curve at 70° C.for a system according to the present invention which contains 58% ofBL036, 2% of the reactive liquid crystalline compound used in FIG. 4 andthe same precursor of the matrix as in the system of FIG. 4.

No memory effect is observed but the saturation voltage is at the sametime considerably increased in comparison to the saturation voltage ofthe system of FIG. 1 as was noted already above. Electrooptical systemsaccording to the present invention,the reactive liquid crystallinecomponent of which amounts are not more than 1% quite generallyrepresent a very low memory effect on the one hand and a small and atany rate tolerable increase of the saturation voltage on the other hand.

Summarizing it can be stated that the electrooptical systems accordingto the present invention are characterized by advantageous eletroopticalproperties and, in particular, by low switching times, especially at lowtemperatures, and a considerably reduced memory effect.

The liquid crystalline mixture used in the electrooptical systemsaccording to the invention contains at lest 2 nonreactive liquidcrystalline compounds which, for the sake of simplicity, are also simplytermed as liquid crystalline compounds. The liquid crystalline mixturepreferably comprises at least one compound of formula I

in which

Z¹ and Z² independently of one another, are a single bond, —CH₂CH₂—,—COO—, CO— or —C═C—,

 independently of one another, are trans-1,4-cyclohexylene,1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene,2,3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene and one of

 may also be pyrimidine-2,5-diyl, pyridine-2,5-diyl ortrans-1,3-dioxane-2,5-diyl,

X¹ and X² independently from one another, are H or F,

Q is CF₂, OCF₂, C₂F₄ or a single bond,

Y is H, F, Cl or CN,

n is 0, 1 or 2, and

R is alkyl having up to 13 C atoms, in which one or two non-adjacent CH₂groups can also be replaced by —O— and/or —CH═CH—.

In the following, for the sake of simplicity, Phe is 1,4-phenylene,Phe.2F is 2-fluoro-1,4-phenylene, Phe.3F is 3-fluoro-1,4-phenylene, Cycis trans-1,4-cyclohexylene, Pyr is pyrimidine-2,5-diyl and Pyd ispyridine-2,5-diyl, the two abbreviations Pyr and Pyd comprising in eachcase the two possible positional isomers. Furthermore, Phe.(F) isintended to designate a 1,4-phenylene group which may be unsubstitutedor monosubstituted by fluorine in the 2 or 3 position. Phe.2F3F andPhe.3F5F are a 1,4-phenylene group which is difluorinated in the 2,and3, and 3 and 5 position respectively. Liquid crystal compounds accordingto formula I, wherein Y is H, F or Cl will be termed in the following asSFM compounds (superfluorinated materials) according to formula I.

Electrooptical systems whose liquid crystal mixture contains one or morebinuclear compounds of the formula 12 are preferred:

In the compounds of the formula 12, R is, preferably alkyl or alkoxyhaving 1-10, but in particular 1-8, C atoms, the straight-chain radicalsbeing preferred. Furthermore, n-alkoxyalkyl compounds and in particularn-alkoxymethyl and n-alkoxyethyl compounds are preferred.

Z² is preferably —CH₂CH₂—, —COO—or a single bond, in particular a singlebond or —CH₂CH₂— and very particularly a single bond. Y is —F, —Cl, —CN,—OCHF₂, —OCF₃ or —CF₃, preferably —F, —Cl or —CN; in case of activelyaddressed PDLC systems according to the present invention Y ispreferably —F, —Cl or —OCF₃.

Compounds of the formula I2 in which at least one of X¹ and X² isdifferent from H are particularly preferred.

is preferably Cyc, Phe.(F), Phe.3F5F, Phe.2F3F, Pyr, Pyd or Dio and inparticular Cyc, Phe.(F), Phe.3F5F, Phe.2F3F, Pyr or Pyd.

Furthermore, electrooptical systems whose liquid crystal mixturecontains one or more trinuclear compounds of the formula 13 arepreferred:

In the compound of the formula I3, R is preferably n-alkyl or n-alkoxyhaving 1-10 C atoms, furthermore also n-alkoxymethyl or n-alkoxyethylhaving 1-8 C atoms and n-alkenyl having up to 7 C atoms.

Very particular preference is given to compounds of the formulae I3 inwhich R is methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl,nonyl, decyl, methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy,heptoxy, octoxy, methoxymethyl, ethoxymethyl, propoxymethyl,butoxymethyl, methoxyethyl, ethoxyethyl or propoxyethyl. Z¹ and Z² inthe compounds of the formulae I3 are, independently of one another,preferably —CH₂CH₂—, —COO— or a single bond and in particular —CHCH₂— ora single bond. Particular preference is given to those compounds of theformula I3 in which at least one of Z¹ or Z² is a single bond. Y is —F,—Cl, —CN, OCHF₂, —OCF₃ or —CF₃ and preferably —F. —Cl, —OCHF₂ or —OCF₃;in case of actively addressed PDLC systems according to the presentsinvention Y is in particular —F, —Cl, —OCHF₂ and —OCF₃.

are, independently of one another, Cyc, Phe.(F), Phe.2F3F, Phe.3F5F,Pyr, Pyd and Dio and in particular Cyc, Phe. (F), Phe.2F3F, Phe.3F5F,Pyr and Pyd.

Furthermore, electrooptical systems whose liquid crystal mixturecontains one or more tetranuclear compounds of the formula I4 arepreferred:

In the compounds of the formulae I4, R is preferably n-alkyl or n-alkoxyhaving 1-10 C atoms, furthermore also n-alkoxymethyl or n-alkoxyethylhaving 1-8 C atoms.

Very particular preference is given to compounds of the formulae I4 inwhich R is methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl,nonyl, decyl, methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxyor octoxy.

In the compounds of the formula I4, preferably not more than 2 and inparticular only one e the bridges Z¹ and Z² are different from a singlebond.

are preferably, independently of one another, Cyc, Phe.2F, Phe.3F, Phe,Pyr or Pyd. Compounds of the formula I4 in which at least one of

is Phe.2F or Phe.3F are preferred. The weight proportion of thecompounds of the formulae I4 in the liquid crystal mixture of theelectrooptical systems according to the invention is preferably not toohigh and is in particular less than 20%, the use of laterallyfluorinated compounds of the formula I4 being in many cases preferred.

The proportion of the compounds of the formula I in the liquid crystalmixtures used according to the invention is preferably not too small andis in particular more than 15% and very particularly more than 20%.Liquid crystal mixtures containing more than 40% and in particular notless than 50% of compounds of the formula I are particularly preferred.

The liquid crystal mixtures used according to the invention can containfurther components which are preferably selected from nematic ornematogenic (monotropic or isotropic) substances, in particularsubstances from the group comprising azoxybenzenes, benzylideneanilines,biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl orcyclohexyl cyclohexanecarboxylates, phenyl or cyclohexylcyclohexylbenzoates, phenyl or cyclohexylcyclohexylcyclohexanecarboxylates, cyclohexylphenylbenzoate,cyclohexylphenyl cyclohexanecarboxylate, or cyclohexylphenylcyclohexylcyclohexanecarboxylate, phenylcyclohexanes,cyclohexylbiphenyls, phenylcyclohexylcyclohexanes,cyclohexylcyclohexanes, cyclohexylcyclohexenes,cyclohexylcyclohexylcyclohexenes, 1,4-bis(cyclohexyl)benzenes,4,4′-bis(cyclohexyl)biphenyls, phenyl- or cyclohexylpyrimidines, phenyl-or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- orcyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes,1-phenyl-2-cy-clohexylethanes,1-cyclohexyl-2-(4-phenylcyclohexyl)ethanes,1-cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes,halogenated or unhalogenated stilbenes, benzyl phenyl ethers, tolans andsubstituted cinnamic acids. The 1,4-phenylene groups in these compoundscan also be fluorinated.

The liquid crystal mixtures used in the electrooptical systems accordingto the invention preferably also contain one or more dielectricallyneutral compounds of the formulae 1-5:

R*—L—E—R**  1

R*—L—CH₂CH₂—E—R**  2

In the formlae 1 and 2 L and E, which may be identical or different, areeach, independently of one another, a bivalent radical from the groupcomprising -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-,-G*-Phe- and -G*-Cyc- and mirror images thereof, Phe being unsubstitutedor fluorine-substituted 1,4-phenylene, Cyc being trans-1,4-cyclohexyleneor 1,4-cyclohexenylene, Pyr being pyrimidine-2,5-diyl orpyridine-2,5-diyl, Dio being 1,3-dioxane-2,5-diyl and G* being2-(trans-1,4-cyclohexyl)ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl or1,3-dioxane-2,5-diyl.

One of the radicals L and E is preferably Cyc, Phe or Pyr. E ispreferably Cyc, Phe or Phe-Cyc. The liquid crystals according to theinvention preferably contain one or more components selected fromcompounds of the formulae 1 and 2, in which L and E are selected fromthe group comprising Cyc, Phe and Pyr and simultaneously one or morecomponents are selected from the compounds of the formulae 1 and 2, inwhich one of the radicals L and E is selected from the group comprisingCyc, Phe and Pyr and the other radical is selected from the groupcomprising -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G*-Phe- and -G*-Cyc-, and,if desired, one or more components are selected from the compounds ofthe formulae 1 and 2, in which the radicals L and E are selected fromthe group comprising -Phe-Cyc-, -Cyc-Cyc-, -G*-Phe- and -G*-Cyc-.

R* and R** in the compounds of the formulae 1 and 2 are each,independently of one another, preferably alkyl, alkenyl, alkoxy,alkenyloxy or alkanoyloxy having up to 8 carbon atoms. In most of thesecompounds, R* and R** are different from one another, one of theseradicals being in particular alkyl, alkoxy or alkenyl.

Especially preferred is the following smaller group of dielectricallyneutral compounds of formulae 3 and 4

wherein

the meaning of R* and R** is the same as given for formulae 1 and 2,

Z* is independently from each other a single bond or —CH₂CH₂—,

1 and m are independently from each other 0 or 1, and

 denotes 1,4-phenylene, 2-fluoro-1,4-phenylene or3-fluoro-1,4-phenylene.

The weight proportion of the compounds of the formulae 1-4 in the liquidcrystals used according to the invention is preferably 0-50% and inparticular 0-40%.

The liquid crystal mixtures used in the electrooptical systems accordingto the invention preferably contain 1-98%, in particular 5-05%, ofcompounds of the formula I. The liquid crystals preferably contain 1-20,but in particular 1-15, and very particularly 1-12, compounds of theformula I.

One skilled in the. art can select additives for the liquid crystalmixtures described from the large pool of nematic or nematogenicsubstances in such a manner that the birefringence Δn and/or theordinary refractive index n_(o) and/or other refractive indices and/orthe viscosity and/or the dielectric anisotropy and/or further parametersof the liquid crystal are optimized with respect to the particularapplication.

The liquid crystal mixture can contain further additives such as, forexample, chiral compounds and other customary additives. Theconcentration of such additives is preferably not more than 7.5% and, inparticular, lower than 5%.

Formula II embraces both known and new reactive liquid crystallinecompounds, and the present invention also relates to the new reactiveliquid crystalline compounds of formula II.

Specifically, the reactive liquid crystalline compounds known so far areoften characterized by high or very high melting points and values ofthe birefringence which are not high enough for many applications.

The present inventors found in extensive investigations that thecompounds according to formula III

R¹—P—X—A³—Z—A⁴—R²  III

wherein

R¹ is CH₂═CW—COO—, CH₂═CH—,

HWN—, HS—CH₂—(CH₂)_(m), COO— with W being H, Cl or alkyl with 1-5 Catoms and m being 1-7,

P is alkylene with up to 12 C atoms, it being also possible for one ormore CH₂ groups to be replaced by O,

X is , —S—, —COO—, OCO— or a single bond,

R² is alkyl radical with up to 15 C atoms which is unsubstituted,mono-or polysubstituted by halogen, it being also possible for one ormore CH₂ groups in these radicals to be replaced, in each caseindependently of one another, by —O—, —S—, —CO—, —OCO—, —CO—O— or—O—COC— in such a manner that oxygen atoms are not linked directly toone another, —ON, —F, —Cl or alternatively R² has one of the meaningsgiven for R¹—P—X,

A³ is a 1,4-phenylene or a napthalene-2,6-diyl radical which both can beunsubstituted or substituted with 1 to 4 halogen atoms, ortrans-1,4-cyclohexylene

A⁴ is

 it being possible for the 1,4-phenylene groups in radicals (a) and (b)to be substituted by CN or halogen and one of the 1,4-phenylene groupsin (a) and (b) can also be replaced by a 1,4-phenylene radical in whichone or two CH groups are replaced by N, and

Z is —CO—O—, —O—CO—, —CH₂CH₂— or a single bond,

exhibit favorable properties and, in particular, advantageous values ofbirefringence and melting point.

Electrooptical systems according to the present invention the reactiveliquid crystalline component of which contains at least one compoundaccording to formula III) exhibit especially advantageous properties.

Formula III covers reactive liquid crystalline compounds with 3 rings offormulae III1-III20

R¹—P—X—Phe′-Z-Phe″-Phe″-R²  III1

R¹—P—X-Phe′-Z-Pyd-Phe″-R²  III2

R¹—P—X-Phe′-Z-Pyr-Phe″-R²  III3

R¹—P—X-Phe′--Z-Phe″-Pyd-R²  III4

R¹—P—X-Phe′-Z-Phe″-Pyr-R²  III5

R¹—P—X-Phe′-Z-Phe″-CH₂CH₂-Phe″-R²  III6

R¹—P—X-Phe′-Z-Pyd-CH₂CH₂-Phe″-R²  III7

R¹—P—X-Phe′-Z-Pyr-CH₂CH₂-Phe″-R²  III8

R¹—P—X-Phe′-Z-Phe″-CH₂CH₂-Pyd-R²  III9

R¹—P—X-Phe′-Z-Phe″-CH₂CH₂-Pyr-R²  III10

 R¹—P—X-Nap′-Z-Phe″-Phe″-R²  III11

R¹—P—X-Nap′-Z-Pyd-Phe″-R²  III12

R¹—P—X-Nap′-Z-Pyr-Phe″-R²  III13

R¹—P—X-Nap′-Z-Phe″-Pyd-R²  III14

R¹—P—X-Nap′-Z-Phe″-Pyr-R²  III15

R¹—P—X-Nap′-Z-Phe″-CH₂CH₂-Phe″-R²  III16

R¹—P—X-Nap′-Z-Pyd-CH₂CH₂-Phe″-R²  III17

R¹—P—X-Nap′-Z-Pyr-CH₂CH₂-Phe″-R²  III18

R¹—P—X-Nap′-Z-Phe″-CH₂CH₂-Pyd-R²  III19

R¹—P—X-Nap′-Z-Phe″-CH₂CH₂-Pyr-R²  III20

In the compounds of formulae III1-III10, Phe′ denotes a 1,4-phenylenegroup

wherein X³-X⁶ denote independently from each other H or halogen;

are preferred.

In the compounds of formulae III1-III20, Phe″ is a 1,4-phenylene group,which is unsubstituted or mono- or polysubstituted by CN or halogen, andin formulae III15-III20, Nap′ is a naphthalene-2,6-diyl group

which is unsubstituted or wherein up to 4 of X⁷-X¹² are independentlyfrom each other halogen while the other denote H.

The compounds of formulae III1-III20 are preferred. Especially preferredare the compounds of formulae III1-III3, III6-III10,III13-III15, andIII18-III20, and, in particular the compounds of formulae III1, III8,III15 and III20.

In the compounds of formulae III1-III20 R¹ is CH₂═CW—COO—, CH₂═CH—,

HWN—, HS—CH₂—(CH₂)_(m)—COO— with W being H, Cl or alkyl with 1-5 C atomsand m being 1-7.

Preferably, R¹ is a vinyl group, an acrylate group, an amino group or amercapto group, and especially preferred are the following meanings ofR¹:

CH₂═CH—COO—  R¹-1

 CH₂═CH—  R¹-4

H₂N—  R¹-5

H(alkyl) N—  R¹-6

HS—CH₂—(CH₂)_(m)—COO—  R¹-7

with alkyl denoting C₁-C₃-alkyl and m being 1-5.

In the compounds of formulae III1-III20, the spacer-type A I group P isalkylene with up to 24 C atoms, it is also being possible for one ormore non adjacent CH₂ groups to be replaced by O.

In case P is alkylene, P may be straight-chain or branched. P especiallypreferred is ethylene,. propylene, butylene, 1-methyl-propylene,2-methyl-propylene, pentylene, 1-methyl-butylene, 2-methyl-butylene,hexylene, 2-ethyl-butylene, 1,3-dimethyl-butylene, hephylene,1-methylhexylene, 2-methylhexylene, 3-methylhexylene, 4-methylhexylene,5-methylhexylene, 6-methylhexylene, octylene, 3-ethyl-hexylene,nonylene, 1-methyloctylene, 2-methyloctylene, 7-methyloctylene,decylene, undecylene, dodecylene, 2-methylundecylene,2,7,5-trimethyl-nonylene or 3-propyl-nonylene.

In case P is mono- or polyoxaalkylene, P may be straight-chain orbranched. In particular, P is 1-oxa-ethylene, 1-oxapropylene,2-oxapropylene, 1-oxa-butylene, 2-oxabutylene, 1,3-dioxabutylene,1-oxa-pentylene, 2-oxa-pentylene, 3-oxapentylene,2-oxa-3-methyl-butylene, 1-oxahexylene, 2-oxa-hexylene, 3-oxa-hexylene,1,3-dioxa-hexylene, 1,4-dioxa-hexylene, 1,5-dioxa-hexylene,1-oxa-heptylene, 2-oxa-heptylene, 1,3-dioxa-heptylene,1,4-dioxa-heptylene, 1,5-dioxa-heptylene, 1,6-dioxa-heptylene,1,3,5-trioxa-heptylene, 1-oxa-octylene, 2-oxa-octylene, 3-oxa-octylene,4-oxa-octylene, 1,3-diooctylene-nonylene, 1,4-dioxa-decylene,1,4-dioxa-undecylene and 1,3,5-trioxa-dodecylene.

X is —O—, —S—, —COO—, —OCO— or a single bond and in particular —O—,—COO—, —OCC— or a single bond. In case X is —O—, —S— or —OCO—, theadjacent CH₂-group of P is not replaced by —O—.

Z is —COO—, —OCO—, —CH₂CH₂— or a single bond. In the compounds offormulae III1-III7 and III15-III19, Z. preferably is —COO—, —OCO—,—CH₂CH₂— or a single bond and, in particular, —COO—, —OCO— or a singlebond. In the compounds of formulae III18-III14 and III20III24 Zpreferably is —CH₂CH₂— or a single bond.

R² can be an alkyl radical with up to 15 C atoms which is unsubstituted,mono- or polysubstituted by halogen, it also being possible for one ormore CH₂ groups in these radicals to be replaced, in each caseindependently from one another, by —O—, —S—, —CO—, —OCO—, —COO— or—O—COO— in such a manner that oxygen atoms are not linked directly toone another.

If R² is an alkyl radical or alkoxy radical, it may be straight-chain orbranched. Preferably, it is straight-chain, A has 2, 3, 4, 5, 6, 7 or 8carbon atoms and accordingly is preferably ethyl, propyl, butyl, pentyl,hexyl, heptyl, octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxyor octoxy, and furthermore methyl, nonyl, decyl, undecyl, tridecyl,tetradecyl, pentadecyl, methoxy, nonoxy, decoxy, undecoxy, dodecoxy,tridecoxy or tetradecoxy.

If R² is oxaalkyl, it is preferably straight-chain 2-oxapropyl(=methoxymethyl), 2-oxabutyl (=ethoxymethyl) or 3-oxabutyl(=2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-,3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-,5-, 6-, 7-or 8-oxanonyl, 2-, 3-, 4-, S-, 6-, 7-, 8-, or 9-oxadecyl.

Preferred branched. radicals R²-are isopropyl, 2-butyl(=1-methylpropyl), isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl(=3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl,2-propylpentyl, 2-octyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy,3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy,1-methylhexoxy, 2-octyloxy, 2-oxa-3-methylbutyl, 3-oxa-4-methylpentyl,4-methylhexyl, 2-nonyl, 2-decyl, 2-dodecyl, 6-methyloctoxy,6-methyloctanyloxy, 5-methylheptyloxycarbonyl, 2-methylbutyryloxy,3-methylvaleryloxy, 4-methylhexanoyloxy, 2-chloropropionyloxy,2-chloro-3-methylbutyryloxy, 2-chloro-4-methylvaleryloxy,2chloro3-methylvaleryloxy, 2-methyl-3-oxypentyl, 2-methyl-3-oxahexyl.

R² can also be a polar terminal group and in particular —CN, —Cl or —F;R² can also be —(L)—C_(d)H_(e)F_(2d+1-e) wherein L is a single bond —O—or —S—, d is 1 or 2 and e is 0, 1, 2, 3, 4 or 5.

R² can also have one of the meanings given for R¹—P—X— above. In case R²is an—optionally substituted—alkyl radical, R¹ preferable is a vinyl oracrylate group while in case R² is R¹—P—X, all meanings given above forR¹ are preferred.

Especially preferred is the following smaller group of reactive liquidcrystalline compounds according to formula III1:

wherein

Y¹ is independently from each other CH₂═CW¹COO—, CH₂═CH— orHS—CH₂—(CH₂)_(m)COO—,

V¹ is independently from each other —O—, —COO—, —OOC—, —S— or a singlebond,

W¹ is independently from each other H, Cl or CH₃,

n is independently from each other 2-12,

m is independently from each other 1-7, and

 is independently from each other 1,4-phenylene, 2-fluoro-1,4-phenylene,3-fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene or2,3,6-trifluoro-1,4-phenylene.

The compounds according to formula III-1 may be laterally unsubstituted(all groups

denote 1,4-phenylene) or 1, 2 or 3 14-phenylene groups may besubstituted independently from each other by 1, 2 or 3 F atoms.Laterally fluorinated compounds are preferred.

Especially preferred are compounds according to formula III-1 wherein Y¹is CH₂═CHCOO, V¹ is O and

is independently from each other 1,4-phenylene or 2-fluoro- or3-fluoro-1,4-phenylene. The compounds of this smaller subclass ofcompounds according to formula II1-1 are characterized by advantageousvalues of birefringence and by low melting points.

Especially preferred is also the following smaller group of compoundsaccording to formula III8:

wherein

Y² is independently from each other CH₂═CHCOO—, CH₂═C(CH₃)—COO— orCH₂═CH—,

V² is independently from each other —O— or a single bond,

n is independently from each other 2-12, and

 has the meaning indicated for III1-1.

The compounds according to this formula may be laterally unsubstituted(all groups

1,4-phenylene) or 1, 2 or 3 1,4-phenylene groups may be substitutedindependently from each other by 1, 2 or 3 F atoms. Laterallyfluorinated compounds are preferred.

Especially preferred are compounds according to formula III8-1 whereinY¹ is CH₂═CH—COO— and V² is —O—. The compounds according to formulaIII8-1 exhibit especially advantageous melting points.

Especially preferred are further compounds according to the followingformula

wherein

Y³ is independently from each other CH₂═CW³COO—, CH₂═CH— orHSCH₂(CH₂)_(m)—COO—,

V³ is independently from each other —O—, —COO—, —OOC—, —S— or a singlebond,

W³ is independently from each other H, Cl or CH₃, a is 0 or 1,

n is independently from each other 2-12,

r is 1 or 2,

m is independently from each other 1-7, and

 has the meaning indicated for III1-1.

Compounds of this type are partially covered by formula III11 (r=2).Particularly preferred are compounds of this type

wherein

Y³ is CH₂═CW³COO—

n is independently from each other 3-11 and in particular 4, 5, 6, 7 or8,

V3 is —O— or a single bond, and

r is 1.

The compounds of this specific subgroup are characterized byadvantageous values of the melting point and the birefringence.

Especially preferred is further the following smaller group of reactiveliquid cystalline compounds according to the following formula

wherein

Y⁴ is independently from each other CH₂═CW⁴COO—, CH₂═CH— orHSCH₂(CH₂)_(m)COO—,

V⁴ is independently from each other —O—, —COO—, OCO—, —S— or a singlebond,

W⁴ is independently from each other H, CH₃ or Cl,

m is independently from each other 1-7,

n is independently from each other 1-12,

t is 0, 1 or 2, and

 has the meaning indicated for III1-1. Compounds of this type are partlycovered by formula III1.

The compounds according to this formula may be laterally unsubstituted(all groups

denote 1,4-phenylene) or 1, 2 or 3 1,4-phenylene groups may besubstituted independently from each other by 1, 2 or 3 F atoms.Laterally fluorinated compounds are preferred.

Particularly preferred is the following rather small group of compounds:

The compounds of this specific subgroup are characterized byadvantageous values of the melting point and the birefringence.

Especially preferred is further the following smaller group of reactiveliquid crystalline compounds according to the following formula

wherein..

Y⁵ is independently from each other CH₂═CW⁵COO—, CH₂═CH— orHSCH2(CH₂)_(m)—COO,

V⁵ is independently from each other —O—, —COO—, —OCO—, —S— or a singlebond,

W⁵ is independently from each other H, CH₃ or Cl,

n is independently from each other 1-12,

m is 1-7,

t and u are independently from each other 0, 1 or 2 with the provisothat t+u 1, 2 or 3,

and

has the meaning indicated for III1-1.

The compounds according to formula III-1 may be laterally unsubstituted(all groups

denote 1,4-phenylene) or 1, 2 or 3 1,4-phenylene groups may besubstituted independently from each other by 1, 2 or 3 F atoms.Laterally fluorinated compounds are preferred.

Compounds of this type are partly covered by formula III1. Particularlypreferred in the following rather small group of compounds:

Especially preferred is further the following smaller group ofcompounds:

Y⁶—T⁶—V⁶—U⁶—V⁶—T⁶—Y⁶

wherein

Y⁶ is independently from each other CH₂═CW⁶COO—l CH₂═CH— orHSCH₂(CH₂)_(m)COO—,

W⁶ is independently from each other H, CH₃ or Cl

T⁶ is independently from each other strait chain (CH₂) or

m is independently from each other 1-7,

n is independently from each other 1-12,

v is independently from each other 1-8,

w is independently from each other 0 or 1,

z is independently from each other 0-4,

V⁶ is independently from each other —O—, —S—, —COO—, —OCO— or a singlebond and, in particular, —O— or —S—

c and d are independently from each other 0, 1 or 2,

c+d is 1, 2 or 3,

X is N or CH, and

 has the meaning indicated for III1-1.

The compounds of this specific subclass are characterized byadvantageous values of the melting point and the birefringence.Compounds wherein T⁶ is

are optically active.

Especially preferred is further the following smaller group of reactiveliquid crystalline compounds

wherein

Y⁷ is CH₂═CW⁷COO—, CH₂═CH—, HSCH₂ (CH₂)_(m)COO—,

Y⁸ has independently of Y⁷ the meaning of Y⁷ or is an alkyl group with1-12 C atoms, which is optionally mono- or polysubstituted by F and/orCl, and/or wherein one or two non-adjacent CH₂ groups may be replaced by—CH═CH—, —O—, —CO—, —COO—, OCO— or —S—,

V⁷ is independently from each other —O—, —COO—, —OOC—, —S— or a singlebond,

W⁷ is independently from each other H, Cl or CH₃,

m is independently from each other 1-7,

b is independently from each other 0-11, and

B is

 with the proviso that in both Y⁷ and Y⁸ are CH₂═CW⁷COO—,

B is

 The meaning of

 is the same as given above.

 comprises all isomers of mono- and difluornated 1,3-phenylene.

The reactive liquid crystalline compounds according to formula I and, inparticular, the preferred compounds according to formula III andaccording to the preferred subclasses can be prepared by methods whichare known per se and which are described, for example, in standard worksof organic chemistry such as, for example, Houben-Weyl, Methoden derOrganischen Chemie, Thieme-Verlag, Stuttgart. Some specific methods canbe taken from the examples.

In the following and in the preceding, all percentages given arepercentages by weight. Temperatures are given in degrees Celsius.

The following examples are intended to illustrate the invention withoutrestricting it.

EXAMPLES Example 1

The reactive liquid crystalline compounds (1)

is prepared via the sequence of reaction steps shown in diagram 1.Pd(Ph) ₃ tetrakis triphenylphosphine palladium and Δ denotes heating.

In step 6 of diagram 1, 1 mol of the phenylether obtained in step 5 and1.1 mol of acryloyl chloride are dissolved in 1 1 of dichlormethane. 1.1mol of triethylamine are added, and the mixture is stirred for 3 hoursat room temperature. Aqueous work-up and column chromatography gives(1).

Example 2

The reactive liquid crystalline compound (2)

is prepared via the sequence of reaction steps shown in diagram 2. TEAis triethylamine, DCM is dichloromethane and rt is room temperature.

In step 4 of diagram 2, 2.2 mol of triethylamine is added dropwise to amixture of 1 mol of the alcohol obtained in step 3, and 2.1 mol ofacryloyl 2 1 of dichloromethane. After 24 hours the reaction mixture iswashed with water, and column chromatography gives (2) .

The following compound are prepared via the sequence of reaction stepsshown in diagram 2a.

Example 3

The reactive liquid crystalline compound (3)

is prepared via the sequence of reaction steps shown in diagram 3 andexhibits the following phase sequence: K 70 S_(A) 140 I.

DME is dimethoxyethane.

In step 5 of diagram 3 2.2 mol of triethylamine is added dropwise to asolution of 1 mol of the hydroxyterphenyl obtained in step 4 of diagram3, and 2.1 mol acryloyl chloride in 2 1 dichloromethane. It is stirredfor 4 hours at room temperature. Aqueous work-up and columnchromatography gives (3).

The following compounds are prepared analogously.

(3.1) exhibits the following phase sequence: K 82.3 I. The carbon atomsdenoted by *, are chiral; (R)(−).

(3.2) exhibits the following phase sequence: K 76.9 S 122.7 I

Melting point of (3.3): K 93 S.

(3.4) exhibits the following phase sequence: K 62 N 81.9 I.

(3.5) exhibits the following phase sequence: K 36.2 S 54.6 N 25 79.6 I.

(3.6) exhibits the following phase sequence: K 94 N 106 I.

(3.7) exhibits the following phase sequence: K 75.3 S 96.9 N 5 104.9 I.

(3.8) exhibits the following phase sequence: K 99.3 N 102.6

(3.9) exhibits the following phase sequence: K 67 I.

(3.10) exhibits the following phase sequence: K 45.6 I.

Example 4

The reactive liquid crystalline compound (4)

is prepared via the sequence of reaction steps shown in diagram 4.

In step 4 of diagram 4, 2.2 mol triethylamine is added dropwise to asolution of the ester obtained in step 3 of diagram 4, and 2.1 molacryloyl chloride in 2 1 dichloromethane. The reaction mixture isstirred at room temperature for 4 hours. Aqueous work-up and columnchromatography gives (4).

The following compounds are prepared analogously.

(4.1) exhibits the following phase sequence: K 87 S_(A) 145 N 170 I.

(4.2) exhibits the following phase sequence: K 44.4 S_(A) 70.2 N 104.5I.

(4.3) exhibits the following phase sequence: K 68 N 133 I.

(4.4) exhibits the following phase sequence: K 45.7 N 75.4 I.

(4.5) exhibits the following phase sequence: K 49.9 N 89.7 I.

Example 5

The reactive liquid crystalline compound (5)

is prepared via the sequence of reaction steps shown in diagram 5.

In step 4, 2.2 mol of triethylamine is added dropwise to a solution of 1mol of the substituted pyrimidine obtained in step 3 of diagram 5, and2.1 mol of acryloyl chloride in 2 1 dichloromethane. The reactionmixture is stirred at room temperature for 4 hours. Aqeous work-up andcolumn chromatographic gives (5).

Example 6

The reactive liquid crystalline compound (6)

is prepared via the sequence of reaction steps shown in diagram 6.

BuLi is buytyllithium and B(OMe)₃ is trimethylborate.

In step 4, 2.2 mol of triethylamine is added dropwise to a solution of 1mol of the substituted pyrimidine obtained in step 3 of diagram 6, and2.1 mol of acryloyl chloride in 2 1 dichloromethane, and the reactionmixture is stirred at room temperature for 4 hours. Aqueous work-up andcolumn chromatography gives (6).

Example 7

The reactive liquid crystalline compound (7)

is prepared via the sequence of reaction steps shown in diagram 7, andexhibits the following phase sequence: K 39 S 58 S′ 85 I (the symmetryof the smectic phases was not determined).

In step 4, 2.2 mol of triethylamine is added dropwise to a solution of 1mol of the ethylene linked compound obtained in step 3 of diagram 4, and2.1 mol of acryloyl chloride in 2 1 dichloromethane. The reactionmixture is stirred for 4 hours at room temperature. Aqueous work-up andcolumn chromatography gives (7).

The following compounds are prepared analogously.

(7.1) exhibits the following phase sequence: K 58 S 80 S′ 107 I (thesymmetry of the smectic phases was not determined).

(7.2) exhibits the following phase sequence: K 53 S_(A) 79.4 I.

(7.3) exhibits the following phase sequence: K 55 S 57 N 62 I.

Example 8

The optically active reactive liquid crystalline compound (8)

is prepared via the sequence of reaction steps shown in diagram 8.

THF is tetrahydrofuran and Br—CH₂—CH₂-THP is2-bromo-1-(tetrahydropyranyl)-ethanol which can be prepared according tothe method described in A. Hoppmann, Tetrahedron, 34 (1978), 1723.

In step 5, 2.2 mol of triethylamine is added dropwise to a solution of 1mol of the diol obtained in step 4 of diagram 8, and 2.1 mol of acryloylchloride in 2 1 dichloromethane. The reaction mixture is stirred at roomtemperature for 4 hours. Aqeous work-up and column chromatography gives(8).

Example 9

The reactive liquid crystalline compound (9)

is prepared via the sequence of reaction steps shown in diagram 9.

Et₃N is (CH₃CH₂)₃ N.

Compound (9) exhibits the following phase sequence:

K 112 N 150 I.

Example 10

The reactive liquid crystalline compound (10)

is prepared via the sequence of reaction steps shown in diagram 10.

Compound (10) exhibits the following phase sequence:

K58 (S 39) I.

Example 11

The reactive liquid crystalline compound (11)

is prepared via the sequence of reaction steps shown in diagram 11.

Compound (11) exhibits the following phase sequence:

K 48.7 I.

What is claimed is:
 1. A reactive liquid crystal compound of formula IIR′-G′—R″  II wherein at least one of terminal groups R′ and R″ is areactive group exhibiting one reaction site selected from HOW′₂C—,HSW′₂C—, HW′N—, a carboxyl group,

 and O═C—N—, or is a polymerizable reactive group exhibiting two or morereactive sites selected from

case independently, H or an alkyl group with 1-5 C atoms, and the otherterminal group of R′ and R″ is an alkyl group of up 15 C atoms which isunsubstituted or substituted by one or more halogens and in which one ormore CH₂ groups is in each case independently replaced by —O—, —S—,—CO—, —OCO—, —CO—O—, or —O—CO—O— wherein O atoms are not directly linkedto one another, G′ is a rod-like diyl group of the formula —S¹—(A⁵Z³)_(m)—A⁶—S²—  wherein S¹ and S² are each alkylene groups with 0-20 Catoms which can be linear or branched, it also being possible for one ormore CH₂ groups to be replaced, in each case independently from eachother, by —O—, —CO—, —S— or —NW′— with the proviso that 0 atoms are notlinked directly to one another, A⁵ and A⁶ are, independently from eachother, a) a cyclohexylene group, wherein one or two non-adjacent CH₂groups may be replaced by O or S atoms, b) an unsubstituted1,4-phenylene group wherein one to three CH groups may be replaced by—N— or a 1,4-phenylene group which is mono- or polysubstituted by F, Cland/or CH₃, c) a bicyclo(2,2,2)octylene group, a naphthalene-2,6-diylgroup, a decahydronaphthalene-2,6-diyl group or1,2,3,4-tetrahydronaphthalene group, Z³ is, independently from eachother, —CO—O—, —O—CO—, —CH₂CH₂—, —CH₂O—, —OCH₂—, —C≡C— or a single bond,and m is 1, 2, 3 or4; wherein at least one of S¹ and S² is an alkylradical with up to 20 C atoms which can be linear or branched andwherein one or more adjacent CH₂ groups are replaced by —CO—O—,—O—CO—NW′—, —NW′—CO—O—or —NW′—CO—NW′, and/or at least one of R′ and R″is an alkyl radical with up to 15 C atoms which is unsubstituted ormono- or polysubstituted by halogen and wherein one or more CH₂ groupsare replaced by —O—CO—O—.
 2. A compound of claim 1, wherein at least oneof S¹ and S² is an alkyl radical with up to 20 C atoms which can belinear or branched and wherein one or more adjacent CH₂ groups arereplaced by —O—, —CO—and —NW′— groups in such a manner that they form agroup —O—CO—O—, —O—CO—NW′—, —NW′—CO—O— or —NW′—CO—NW′.
 3. A compound ofclaim 2, wherein at least one of S¹ and S² contains a group —O—CO—O—. 4.A compound of claim 2, wherein R″ is an alkyl radical with up to 15 Catoms which is unsubstituted or mono- or polysubstituted by halogen andwherein one or more CH₂ groups is replaced by —O—CO—O—, and S² is asingle bond.
 5. A compound of claim 1, wherein one of R′ and R″ is areactive group and the other is an alkyl radical with up to 15 C atomswhich is unsubstituted or mono- or polysubstituted by halogen andwherein one or more CH₂ groups are replaced by —O—CO—O—.
 6. A compoundof claim 1, wherein —(A⁵—Z³)_(m)A⁶— is of formula (1), (2) or (3):—A⁵—Z³—A⁶—  (1) —A⁵Z³—A⁵Z³—A⁶—  (2) —A⁵—Z³ ⁻A⁵—Z³—A⁵—Z³—A⁶—  (3).
 7. Acompound of claim 1, wherein —(A⁵—Z³)_(m)A⁶— is of the formulae:-Phe-Z³-Phe-  (2)a -Cyc-Z³-Cyc-  (2)b -Phe-Z³-Cyc-  (2)c-Pyr-Z³-Phe-  (2)d -Pyd-Z³-Phe-  (2)e -Dio-Z³-Cyc-  (2)f-Phe-Z³-Phe-Z³-Phe-  (3)a  -Cyc-Z³-Phe-Z³-Phe-  (3)b-Cyc-Z³—Cyc-Z³-Phe-  (3)c -Cyc-Z³—Cyc-Z³—Cyc-  (3)d-Pyr-Z³-Phe-Z³-Phe-  (3)e -Pyd-Z³-Phe-Z³-Phe-  (3)f wherein, Phe is1,4-phenylene which is unsubstituted or mono-, di- or trifluoronated,Cyc is 1,4-cyclohexylene, Dio is 1,3-dioxane-2,5-diyl, Pyd ispyridine-2,5-diyl, and Pyr is pyrimidine-2,5-diyl.
 8. A compound ofclaim 1, wherein Z³ is —COO—, —OCO—, —CH₂CH₂—, —C≡C— or a single bond.9. A compound of claim 7, wherein Z³ is —COO— or —OCO—.
 10. A compoundof claim 7, wherein the two Z³ groups in formulae (3)a-(3)f are asfollows: a) the first Z³ is a single bond and the second Z³ is a singlebond; b) the first Z³ is a single bond and the second Z³ is —CH₂CH₂—; c)the first Z³ is —CH₂CH₂—and the second Z³ is —CH₂CH₂—; or d) the firstZ³ is —OCO—and the second Z³ is —COO—.
 11. A compound of claim 1,wherein at least one of R′ and R″ is a reactive group selected fromH₂C═CH—COO—, H₂C═C(CH₃)—COO—, H₂C═CH—, HS—CH₂—,


12. A compound of claim 11, wherein m is 1 or 2, A⁵ and A⁶ are eachindependently 1,4-phenylene that is unsubstituted or mono- orpolysubstituted by F, Cl or CH₃, and Z³ is —COO—, —OCO—, —CH₂CH₂—,—C═—C— or a single bond.
 13. A compound of claim 12, wherein m is 1 or2, A⁵ and A⁶ are each independently 1,4-phenylene that is unsubstituted,mono- or disubstituted by F, Cl or CH3 and Z³ is —COO— or —OCO—.
 14. Aliquid crystalline mixture comprising at least two liquid crystallinecompounds, at least one of which is a compound of claim
 1. 15. A liquidcrystalline mixture comprising at least two liquid crystallinecompounds, at least one of which is a compound of claim
 1. 16. A mixtureof claim 14, further comprising at least one liquid crystalline compoundof formula II′ R′-G′-R″  II′ wherein one of terminal groups R′ and R″ isa reactive group exhibiting one reaction site selected from HOW′₂C—,HSW′₂C—, HW′N—, a carboxyl group,

 and O═C—N—, or is a polymerizable reactive group exhibiting two or morereactive sites selected from

case independently, H or an alkyl group with 1-5 C atoms, and the otherterminal group of R′ and R″ is an alkyl group of up 15 C atoms which isunsubstituted or substituted by one or more halogens and in which one ormore CH₂ groups is in each case independently replaced by —O—, —S—,—CO—, —OCO—, —CO—O—, or —O—CO—O—wherein O atoms are not directly linkedto one another, G′ is a rod-like diyl group of the formula—S′—(A⁵—Z³)_(m)—A⁶—S²—  wherein S¹ and S² are each alkylene groups with0-20 C atoms which can be linear or branched, it also being possible forone or more CH₂ groups to be replaced, in each case independently fromeach other, by —O—, —CO—, —S— or —NW′— with the proviso that 0 atoms arenot linked directly to one another, A⁵ and A⁶ are, independently fromeach other, a) a cyclohexylene group, wherein one or two non-adjacentCH₂ groups may be replaced by O or S atoms, b) an unsubstituted1,4-phenylene group wherein one to three CH groups may be replaced by—N— or a 1,4-phenylene group which is mono- or polysubstituted by F, Cland/or CH₃, c) a bicyclo(2,2,2)octylene group, a naphthalene-2,6-diylgroup, a decahydronaphthalene-2,6-diyl group or1,2,3,4-tetrahydronaphthalene group, Z³ is, independently from eachother, —CO—O—, —O—CO—, —CH₂CH₂—, —CH₂O—, —OCH₂—, —C≡C— or a single bond,and m is 1,2,3 or
 4. 17. A mixture of claim 16, wherein said otherterminal group of said at least one compound of formula II′ is F, Cl,CF₃, OCF₃, OCHF₂ or nonpolar alkyl or alkoxy with up to 15 C atoms. 18.A mixture of claim; further comprising at least one liquid crystallinecompound of formula II″ R′-G′-R″II″ wherein both of terminal groups R′and R″ are each independently, a reactive group exhibiting one reactionsite selected from HOW′₂C—, HSW′₂C—, HWN—, a carboxyl group,

 and O═C—N— or is a polymerizable reactive group exhibiting two or morereactive sites selected from

case independently, H or an alkyl group with 1-5 C atoms, G′ is arod-like diyl group of the formula S′—(A⁵Z³)_(m)—A⁶S²  wherein S¹ and S²are each alkylene groups with 0-20 C atoms which can be linear orbranched, it also being possible for one or more CH₂ groups to bereplaced, in each case independently from each other, by -O—, —CO—, —S—or —NW′— with the proviso that O atoms are not linked directly to oneanother, A⁵ and A⁶ are, independently from each other, a) acyclohexylene group, wherein one or two non-adjacent CH₂ groups may bereplaced by O or S atoms, b) an unsubstituted 1,4-phenylene groupwherein one to three CH groups maybe replaced by —N— or a 1,4-phenylenegroup which is mono- or polysubstituted by F, Cl and/or CH₃, c) abicyclo(2,2,2)octylene group, a naphthalene-2,6-diyl group, adecahydronaphthalene-2,6-diyl group or 1,2,3,4-tetrahydronaphthalenegroup, Z³ is, independently from each other, —CO—O—, —O—CO—, —CH₂CH₂—,—CH₂O—, —OCH₂—, —C≡C— or a single bond, and m is 1,2,3 or
 4. 19. Amixture of claim 14, comprising not more than 10 reactive liquidcrystalline compounds.
 20. A mixture of claim 14, further comprising oneor more compounds of formula I

wherein Z¹ and Z² independently of one another, are each a single bond,—CH₂CH₂—, —COO—, —OCO— or —C═C—,

 independently of one another, are each trans-1,4-cyclohexylene,1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene,2,3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene, and one of

 can also be pyrimidine-2,5-diyl, pyridine-2,5-diyl ortrans-1,3-dioxane-2,5-diyl, X¹ and X² independently from one another,are each H or F, Q is CF₂, OCF₂, C₂F₄ or a single bond, Y is H, F, Cl orCN, n is 0, 1 or 2, and R is alkyl having up to 13 C atoms, in which oneor two non-adjacent CH₂ groups are, optionally, replaced by —O— and/or—CH═CH—.